* {
    padding: 0;
    margin: 0;
    list-style: none;
}
.banner {
    margin: 100px auto;
    border: 5px solid #000;
    width: 100%;
    height: 640px;
    position: relative;
    overflow: hidden;
}
.banner .img {
    width: 5000px;
    position: absolute;
    left: 0px;
    top: 0px;
}
.banner .img li {
    float: left;
}
.banner .img li img {
    width: 100%;
}
/*小圆点的样式*/
.banner .num {
    position: absolute;
    right: 40px;
    bottom: 30px;
}
.banner .num li {
    width: 20px;
    height: 20px;
    float: left;
    background: #333;
    margin-left: 20px;
    border-radius: 50px;
    border: 2px solid white;
}
.banner .num li.on {
    border: 2px solid #333;
    background: white
}
/*两边耳朵的样式*/
.banner .btn {
    position: absolute;
    width: 80px;
    height: 80px;
    background: rgba(0, 0, 0, 0.7);
    font-size: 60px;
    color: white;
    text-align: center;
    line-height: 80px;
    top: 50%;
    margin-top: -80px;
    cursor: pointer;
    display: none;
}
.banner:hover .btn {
    display: block;
}
.banner .btn_l {
    left: 10px;
    border-radius: 50%
}
.banner .btn_r {
    right: 10px;
    border-radius: 50%
}